In many industries and applications, a coating, or film, is formed on a substrate. The coating may be part of a layered fabrication process, such as in semiconductor fabrication applications, or a barrier to protect the substrate, such as paint and anodizing. In many applications, the thickness of the coating must be measured.
Conventional measurement systems for measuring the thickness of a coating are generally destructive or non-destructive. Conventional destructive measurement systems often examine a random sample during production of the coated parts. The sample is cut or otherwise destroyed in order to produce a cross-sectional view of the coating that can then be physically measured. Conventional destructive measurement systems have the disadvantage of destroying a representative sample of the coated parts, thereby increasing the production cost of the coated parts. In addition, destructive measurement systems assume that the thickness of the coating on the sample is the same as the coating thickness on the other coated parts. Accordingly, the coating thickness on each coated part is not measured and verified.
Conventional nondestructive measurement systems are often used to measure very thin layers during semiconductor fabrication processes. In particular, semiconductor fabrication processes generally measure thicknesses on the order of 1,000 Angstroms or less. Some conventional nondestructive measurement systems utilize a spectral imaging system to measure the reflectivity properties of light that is reflected off the thin film. Optics are generally used to focus the light at a normal angle onto the thin film. The reflected light may then be collected by the same optics and directed to a spectrometer to measure the spectral properties of the reflected light. The spectral properties of the reflected light are indicative of the thickness of the thin film.
Conventional nondestructive measurement systems do not accurately measure the thickness of films and coatings having a thickness on the order of one micron and greater. In addition, conventional nondestructive measurement systems are not particularly suited for measuring film and coating thicknesses on parts larger than semiconductor wafers. Furthermore, many conventional nondestructive measurement systems are particularly adapted to measure only transparent and semitransparent films. In particular, conventional nondestructive measurement systems, such as eddy current testing, cannot accurately measure the thickness of anodized coatings.